This invention relates generally to gas turbine components, and more particularly to turbine shrouds and related hardware.
It is desirable to operate a gas turbine engine at high temperatures for efficiently generating and extracting energy from these gases. Certain components of a gas turbine engine, for example stationary shrouds segments and their supporting structures, are exposed to the heated stream of combustion gases. The shroud is constructed to withstand primary gas flow temperatures, but its supporting structures are not and must be protected therefrom. To do so, a positive pressure difference is maintained between the secondary flowpath and the primary flowpath. This is expressed as a back flow margin or “BFM”. A positive BFM ensures that any leakage flow will move from the non-flowpath area to the flowpath and not in the other direction.
In prior art turbine designs, various arcuate features such as the above-mentioned shrouds, retainers, and supporting members are designed to have matching circumferential curvatures at their interfaces under cold (i.e. room temperature) assembly conditions. During hot engine operation condition, the shrouds and hangers heat up and expand according to their own temperature responses. Because the shroud temperature is much hotter than the hanger temperature and the shroud segment is sometimes smaller than the hanger segment or ring, the curvature of the shroud segment will expand more and differently from the hanger curvature at the interface under steady state, hot temperature operation conditions. In addition, there is more thermal gradient within the shroud than in the hanger, resulting in more deflection or cording of the shroud.
Because of these curvature differences between the shroud support rails and hanger support rails at the interface, a leakage gap is formed between the hanger support rail and the shroud support rail which can cause excessive leakage of cooling air at the shroud trailing edge and lower the BFM at the shroud leading edge, significantly increasing the risk of localized ingestion of hot flow path gases. These curvature deviations also can create stresses on the shroud at the hot temperature condition, lowering the life of the shroud.
Accordingly, there is a need for a shroud design that can reduce the curvature deviation between the shroud support rail and the hanger support rail at the hot operation condition, minimizing the risk of adverse impact to both shroud and hanger durability.